The present invention relates to a stator structure of an electric rotary machine and more particularly, to attachment of inter-phase insulating layers which are interleaved, in the vicinity of the stator outer end surface, between different phases of the stator winding of a high voltage and small-sized motor.
In the high voltage and small-sized motor to be applied with a phase voltage of more than 300 volts, corona discharge may often occur between different phase coils of the stator winding in the vicinity of the stator outer end surface. Such a corona discharge causes rapid deterioration in insulating coatings of the coil wire conductors and eventual layer short-circuiting thereat, frequently resulting in burning troubles of motors. This is attributable to the fact that the insulating coating, for example, enamel coating of the wire conductor undergoes rapid deterioration when the applied voltage exceeds 350 to 370 volts. In order to prevent the insulation deterioration due to the corona discharge, according to well known practice, insulating layers made of polyester such as a product sold under a trade mark of "Mylar" manufactured by Du Pont are interleaved between different phase coils of a stator winding portion in the vicinity of the stator outer end surface (this stator winding portion being referred to as coil structure end portion hereinafter). For example, U.S. Pat. No. 3,038,093 to Robert L. Needham et al discloses the manner in which a plurality of pieces of insulating member are applied at sites selected for insulation purposes.
Generally, in the type of lap winding whose winding is effected manually, the attachment of the inter-phase insulating members is relatively easy. But, because of extremely poor efficiency in work of winding and consequent high cost, lap winding is employed only for the small scale production, for example, production of large-size electric rotary machines.
Therefore, for the large scale production, concentric winding is usually employed which is suitable for winding by means of winding machine with high efficiency in work of winding. To conform to concentric winding, as will be detailed later, an attempt to use insulating strap layers as the inter-phase insulating members for the coil structure end portion was made, in which the insulating strap layers which extend in the circumferential direction of the stator were interleaved between different phase coils in the vicinity of the stator outer end surface. This attempt ensures that the insulating strap can be interleaved completely between different phase coils before the coil structure end portion is forced to deform radially and outwardly of the stator for its shaping and the insulating strap and a bundle of coil wire conductors are then bound with binding yarns. When bound with the binding yarns, however, the insulating strap is also shifted or displaced in part radially and outwardly and as a result, it cannot be interleaved completely or fitted between different phase coils any more. Consequently, as will be detailed later, insulating coatings of wire conductors of different phase coils come in direct contact with each other in the vicinity of the stator outer end surface and corona discharges will occur. For these reasons, rapid deterioration in coil insulation was experienced, resulting in decrease in lifetime of the product or, to extremities, defective products.
Additionally, as will be detailed later, another attempt to use comb-shaped insulating straps each having a plurality of integral projections at its side edge close to the stator outer end surface was made, in which the comb-shaped insulating straps were interleaved between different phase coils by deeply inserting the projections into spaces between different phase coils or into slots of the stator. This attempt ensures that the insulating strap, when bound with binding yarns, will not be displaced radially and outwardly of the stator in contrast to the former attempt, thereby preventing deterioration in insulation of coatings of the coil wire conductors which is caused by corona discharges. However, roots of the projections of the comb-shaped insulating strap were liable to be damaged mechanically, resulting in difficulties with interposition of the strap between different phase coils. With thick comb-shaped insulating straps of increased mechanical strength, it was possible to interleave the thick straps between different phase coils with ease; but when interleaved between different phase coils extending around the circumference of the stator, the thick insulating strap of less flexibility prevented the phase coils from being smoothly shaped radially and outwardly of the stator. If shaped, the phase coils experienced to recover inwardly.